Rubber processing composition



Patented Nov. 17, 1953 UNITED RUBBER PROCESSING COMPQSI'HON Walter A.Schulse, Bartlesvllle, kla., assignor to Phillips Petroleum Company, acorporation of Delaware No Drawing. Application August 15, 1949,

Serial No. 110,479.

13 Claims. (01. 106-218) This invention relates to rubber processingcompositions. In one embodiment it relates to a composition comprisingliquid polymers of a conjugated diolefln and a rosin acid, In onespecific embodiment this invention relates to novel rubber processingcompositions made of liquid polymers of butadiene and rosin acid.

In the manufacture of rubber products, compounding and processing havebecome complicated by the numerous additive agents which are required toimpart the desired properties to the finished articles. It is generallynecessary that a softener or plasticizerbe present, as well as othersubstances, which will aid the vulcanization process. For the latterpurpose, an organic acid is one of the materials frequently employed.Substances which improve tensile strength, tack. abrasion resistance,and control the cure are also considered essential in many instances. Inthe processing of natural rubber scorching has been one of thedifficulties encountered and additive agents which will effectimprovements in this respect are highly desirable. It is known thatcertain advantages are gained through the presence of rosin acid inrubber products but the incorporation of rosin acid into polymericmaterials presents numerous difficulties. It is difilcult to incorporaterosin acid into rubber on the mill,

In the production of synthetic rubber, an alkali metal salt of rosinacid is frequently employed as the emulsifying agent for carrying outpolymerization reactions. but its use in this capacity is limitedsinceit is not applicable in some poly= merization recipes, particularly atlow temperatures. Rosin soap may be addedto the latex and aftercoagulation rosin acid will remain in the product. This method, whichrequires an alkali to convert the acid to the corresponding salt and anacid to convert the salt back to the rosin acid during coagulation ofthe latex, is obviously not economical but it has afforded a means ofproducing rosin acid rubber.

I have now discovered novel rubber processing compositions which furnisha convenient and economical method for incorporating rosin acid directlyinto rubber on the mill and which simultaneously provide the acidnecessary for vulcanferred to as vulcanizable plasticizer compositions.areprepared from a low molecular weight or liquid butadienepolymefandrosin acid. With the discovery of the rubber processingmaterials of this invention, much less complicated com Y of rubber andrubber-like materials, said compoizationtogether withthe softeningorplasticiz- I ing agent, the latter being in itself vulcanizable.

These compositions, which are hereinafter resitions comprising a productobtained by the reaction of a liquid polymer of a conjugated dioleflnwith rosin acid.

still another object is to provide rubber products of improvedproperties by a process which comprises the incorporation ofvulcanizable plasticizer compositions therein, said compositionscomprising a reaction product'of a liquid polymer of butadiene and rosinacid.

Still another object of this invention is to provide a process for theproduction of improved rubber and rubber-like materials containing rosinacid wherein the rosin acid is incorporated into said rubber andrubber-like materials by the use of novel vulcanizable plasticivercompositions.

Further objects-and advantages of this invention will be apparent to oneskilled in the art from the accompanying disclosure and discuss on.

The foregoing ob ects, apply, collectively and severally, to naturalrubber and to various synthetic rubbers. The term rubber" herein whenused alone. without reference to either natural rubber or syntheticrubber, is intended to generically represent bothnatural rubber andsynthetic rubber. Another generic term that has been applied to thesematerials is "a vulcanizable organic plastic substance containingunsaturated carbon to carbon bonds.

The butadiene polymer-rosin acid compositions of this invention arepowerful plasticizers as evidenced by their effect on difil'cultlyprocessablc synthetic elastomers. A rubber polymeric material having ahigh Mooney value can be softened readily through the incorporation ofthese additive agents and the processing characteristics are greatlyimproved. These novel compositions, also. act as cure retarders, thusmaking it possible to overcome deleterious effects which result in someinstances from too rapid cure. The effects on scorch characteristics areespecially important, particularly in the processing of natural rubber.Indeed one of the important advantages oi the additive compositionsherein described is their action as scorch retarders. Another advantageis the improvement in abrasion resistance which is shown in both naturaland synthetic rubber stocks.

The vulcanizable plasticizer compositions of this invention are preparedfrom a low molecular weight butadiene pol mer and rosin acid. They arehomogeneous materials which vary in viscosity from very viscous orsemisolid substances to fluid com ositions depending upon the viscosityof the butadiene polymer and the proportion of butadiene to rosin acidem loyed. The proportions of the ingredients m y be varied over broadranges to give compositions which are readily incorporated into rubberon the mill.

The polymers employed in the preparation of the additive agents arereferred to as butadiene polymers and t is term includes polymers of1,3-butadiene, which is the preferred species, and various other coniuated d oleflns which may be considered as substituted 1.3-butadienes. Eam les of other diolefins include isoprene, piperylene. and2,3-dimethvl-1i i-butad ene. It is preferable that the coniu ateddiolefin contain not more than 6 carbon atoms per molecule. In the prearat on of low molecular wei ht polymers. Iii-butadiene. or a relateddiolefln, such as rev ously mentioned. is polymerized alone or with amonomer cooolvmerizable therewith, with the butadiene compri ng the maor polymerizahle ingredient and being present in an amount which exceeds50 per cent bywei ht ofthe monomeric material. Comonomers include v nvlcom ounds, such as stvrene, m thyl substituted stvrenes, and the l ke,as well as conju ateri diolefins. such as iso rene. pipervlene,2.3-dimethyl-l,3-butadiene, and the like. While the polymers may beprepared by any method which will yield a l quid product, masspolymerization is generally preferred. When mass polymerization methodsare em loyed. liouid products are read ly obtained by controlling thetemperature, pressure. amount of catalyst. kind and amount of solvent.and the like, with no additional materials being necessary to regulatethe viscosity. If desired. the liquid polymers may be prepared byemulsion polymerization but in such cases it is necesary to employmodifiers in order to obtain a product of the viscosity desired. Thou hmass polymerization and emulsion polymerization techniques are wellknown in the art the following mass polymerizat on procedure, forexample, may be employed for making the polymer material to be used inpreparing the vulcanizable composition oi the present invention.Butadiene is pol merized in the presence of finely divided metallicsodium as a catalyst. the amount of sodium" used usually falls withinthe range of 4 to 10 parts by weight per 100 parts by weight ofbutadiene. such as butane, may be used if desired. The polymerizationtemperature is held within the range of 80 to 120 C., and a pre suresufllcient A diluent,

to maintain liquid phase in the reaction system is generally employed.The reaction time is within the range of 4 to 10 hours. After thepolymerization reaction is completed the buta diene polymer is separatedfrom unreacted butadiene and metallic sodium.

'Rosin acids obtained from various sources, such as wood rosins and gumrosins, are applicable in this invention. Also, the disproportionatedacids derived from rosin, such as abietic acid, dehydroabietic acid,tetrahydroabetic acid, and mixtures of these acids, may be employed.

As hereinbefore mentioned, the butadiene polymers employed in thepreparation of the vulcanizable plasticizer compositions of thisinvention are low molecular weight or liquid poly mers. The viscosity ofthese materials may vary within wide limits but usually ranges between1,000- and 30,000 Saybolt Universal seconds at 100 F. However, anybutadiene polymer of low molecular weight, that is, a liquid polymer, isapplicable in this invention.

In the vulcanizable plasticizer compositions herein described, theproportion of rosin acid to butadiene polymer may vary over a broadrange but will usually not exceed a 1:1 ratio, and usually the ratio inthe range of 0.3 to 1.0 part rosin acid per part polymer by weight ispreierred. No definite limits can be set, however, since the proportionsof ingredients will be governed by the rubbersample in which thecomposition is incorporated as well as the properties desired in theproduct. A composition that will flow is generally preferred to one ofthe more viscous type. The liquid polymer and rosin acid may be admixedor possibly reacted in any suitable manner to form the vulcanizablecomposition, but it is preferred to agitate them in a suitable containermaintained at a temperature in the range of about 20 to C. for a, periodof 5 minutes to 1 hour, or until a homogeneous product is obtained.Applicant does not wish to be bound by any specific theory concerningthe mechanism of the formation of his novel plasticizer composition.However, it is possible that a chemical reaction takes place betweenthese two reactants and that one or more definite chemical compounds arethus formed.

The amount of plasticizer composition employed for a given processingoperation is governed by the type of rubber to be processed and theresults desired. Usually, however, it is desirable to use 5 to 40 partsby weight of the preferred polymer-rosin acid composition to parts byweight of the rubber or rubber-like material to be processed.

As hereinbefore stated, the compositions of this invention areapplicable when processing both natural and synthetic rubber stocks andnumerous advantages have been presented. These advantages areillustrated further in the examples, which should not be interpreted inany way to unnecessarily limit the invention.

EXAMPLE 1 A composition was prepared comprising two parts by weight ofsodium polymerized liquid polybutadiene admixed with one part by weightof rosin acid and the resulting mixture agitated at about 25 C. forabout 30 minutes. This resulting material was used in the compoundingrecipes of Table I in which natural rubber was employed. A controlrecipe using asphalt softener is also included. The quantities are givenas parts by weight.

Stearic acid activator was included in the control recipe to supply acidcomparable in amount to the rosin acid in the vulcanizable plasticiaercompositionused in recipe I. The polybutadiene-rosin acid compositionincorporated-into the rubber samples very rapidly. Curing was effectedat 307 F. Tests were made on all samples at equal states of cure asdetermined by compression set data. The polybutadiene-rosin acidcomposition exhibited a pronounced plasticizing action, retarded therate of cure, and improved the scorch properties. On account of itssoftening actionthe hardness of the stock was decreased.Improvementswere also realized in abrasion resistance. -The resultsshownin Table II were obtained:

Table II I 11 Control Unaged Samples:

Minutes to cure to 18%compression set 40 40 29 Compounded Mooney, MS 1%31 27 35.5 Shore hardness 50 50 Abrasion loss. cc. (35 minute cnre).. 3.22 3. 6B 3. 98 Minutes to scorch at 250 F. 16 18 Oven Aged 24 Hours at212 F.:

Shore hardness 54 54 62 Abrasion loss, cc. (35 minute cure) a 3. 90 5.67

EXAMPLE n Three runs were made to determine the effect of stearic acidon the rate of cure and also on the scorch properties when included in acompounding recipe using a polybutadiene-rosin acid composition as thesoftener. compounding recipe I of Example I was used, one withoutstearic acid and the other with 3.0 parts by weight of this additive,but each containing 9.0 parts by weight of the polybutadiene-rosin acidcomposition. A run was also made using the control recipe of Example Iin which 6.0 parts by weight of an asphalt softener and 3.0 parts byweight of stearic acid were employed. The rate of cure is shown bycompression set data, an activating-eflect being obtainedin the samplescontaining the stearic acid. When stearic acid is present, the curingrate with the polybutadienerosin acid softener is similar to 'what isobtained with the asphalt softener but a noticeable difference isobserved in scorch properties, the former serving as a'scorch retarder.The data are shown in Table III, with runs being designated as follows:Run 1, 9.0 parts by weight polybutadienerosin acid composition, nostearic acid; run II,

In two runs the 9.0 parts by weight polybutadiene-rosin acid com-'position, 3 parts by weight stearic acid; run 111,

6.0 parts by weight asphalt softener, 3 parts by weight stearic acid(control). x

The'liquid polybutadiene-rosin acid composition of Example I wascompounded with natural rubber according to the recipe in Table IV-(desi"g'nated as I) and the resulting sample evaluated. A similarevaluation was made substituting an asphalt softener for thepolybutadiene-rosin acid composition (designated as II in Table IV). The.quantities are givenas parts by weight.

Table I V I II Natural rubber 100 Carbon 13 r j 50 50 Zinc oxide 4 V 4Stearic ac 3 3 Sulfur. 2 2 N-cyciohox yi-2-ben zothiazole-sulienamlde 0.4 0. 4 Phenyl-beta-naphthylamine l. 6 1. 5 Polybutadienc-rosin acidcomposition. 6 Asphalt softener 0 Curing was eifected at 307 F. Testswere made on samples at equal states of cure, as determined bycompression set data. The polybutadienerosin acid composition exhibiteda greater plasticizing effect than the asphalt softener and showedimprovements in hysteresis properties and abrasion resistance. The dataare herewith presented in Table V.

Table, V

Unaged Samples:

Minutes to cure to 17.5% com ression set compounded Mooney, MS 1Hysteresis. AT. F. (30 minute cure) Resilience. percent Abrasion loss,grams (30 minute cure) Flex life, percent broken at 50,000 fiexurcs.Oren Aged 24 Hours at 212 F.:

Hysteresis, AT, F. (30 minute cure) Resilience, percent Abrasion loss,grams (30 minute cure) EXAMPLE IV polybutadiene-rosin acid composition.

Table VI Parts by weight Butadiene styrene copolymer 100 Carbon black 50Zinc oxide 3 Polybutadiene-rosin acid composition 9 Sulfur 1.75

N-cyclohexyl-z-benzothiazolesulfenamide 0.95

r 7 Curing was effected at 307 F. Tests were made on the samples atequal states of cure as determined by compression set data. Results ofthe tests are shown in Table VII. The polybutadiene- 'rosin acidcomposition exhibited excellent plasticizing properties, as evidenced bythe compounded Mooney value (MS 1%). Samples containing this softeneralso showed improved resilience and abrasion resistance and handed wellon the mill.

EXAMPLE V Two recipes were employed for compounding samples of abutadiene-styrene copolymer prepared by emulsion polymerization at 41 F.The polymer, prior to compounding, had a. Mooney value of 64 (ML4). Inone case the liquid polybutadiene-rosin acid composition described inExample I was employed as the softener while in the other case anasphalt softener was used. The compounding recipes are presented inTable VIII, the quantities being given as parts by weight.

Table VIII Poiybutadiene-Rosin Asphalt Acid Softener SoftenerButndicne-styrcnc copolymer 100 100 Carbon black 50 60 Softener 10 10Zinc oxide 3 3 Stoaric acid 1 1 Sulfur 1. 75 1. 5N-eyclohcxyi-Z-benzothiazolcsuifenainide- 0. 95 0. 95

The samples were cured 30 minutes at 307 F. The data contained in TableIX were obtained.

Table IX Polybutadlene-Rosin Asphalt Acid Softener Softener UnusedSamples:

Compoundcd Mooney, MS 1% 42 50. 5 Stress-strain properties at 80 F.

'300% modulus, p. s. i.. 1,030 1,140 Tensile, p. s. l 3, 460 3,550Elongation, pcrcent 675 076 Stress-strain properties at 200 F.

'lcnsilc, p. s. i 2, 120 2,000 Elongation, percent 425 475 Resilience,percent 65.0 64. 0 Flex life at 210 F., thousands of ii to failure 16. 943. 8 Abrasion loss, grams (35 minute cure). 2. 50 2. 81 Oven Aged 24Hours at 212 F.:

Stress-strain properties at 80 F.-

300% modulus, p. s. i 2,110 2,090 'Iensilc, p. s. i 4,130 3, 460Elongation, percent 500 460 Resilience, percent 60.2 60.0 Flex life at210 F,, thousands of flexures to failure 13.5 8.9 Abrasion loss, grams(35 minute cure). 2. 56 3. 58

The vulcanizable softener (polybutadiene-rosin acid composition) showedmuch greater plasticizing effects than the asphalt softener as evidencedby the decrease in Mooney values upon compounding. The retention of flexlife on oven aging is particularly noteworthy, the sample containing thevulcanizable softener showing about an 80 per cent retention of flexlife while a value of only around 20 per cent was shown with the samplecontaining the asphalt softener.

' It is to be understood that this invention should not be unnecessarilylimited to the above discussion and description and that modificationsand variations may be made without departing from the invention or fromthe scope of the claims.

The present application claims the compositions of liquid polymer androsin acid. Claims to making rubber processing compositions from thecompositions claimed herein plus rubber, and the resulting rubbercompositions, are claimed in November 8, I951.

I claim: 1. g

1. A rubber vulcanizing composition consisting essentially of anadmixture of (a) a liquid polymer prepared by sodium catalyzed masspolymerization of a conjugated diolefin having not more than 6 carbonatoms per molecule with (b) a rosin acid.

2. A rubber vuicanizing composition comprismy copending applicationSerial No. 255,518 filed ing an admixture of one part by weight of aliquid polymer of aconjugated diolefin having not more than 6 carbonatoms per molecule with 0.3 to 1 part of rosin acid.

3. A composition of claim 2 wherein the conjugated diolefin is1,3-butadiene.

4. A composition of claim 2 wherein said rosin acid is adisproportionated rosin acid.

5. A composition of claim 2 wherein said composition is produced byheating said liquid polymer and rosin acid at 20 to C. for five minutesto one hour.

6. A composition of claim 2 wherein said con- .lugated diolefin is1,3-butadiene, and wherein the viscosity of said liquid polymer iswithin the range of 1000 to 30,000 Saybolt Universal seconds at F.

'7. A composition of claim 2 wherein said liquid polymer is obtained by.sodium catalyzed mass polymerization of 1,3-butadiene.

8. A rubber vulcanizing composition consisting essentially of anadmixture of (a) a liquid polymer prepared by sodium catalyzed masspolymerization of 1,3-butadiene with (b) a rosin acid.

9. A rubber vulcanizing composition comprising an admixture of a liquidpolymer of a conjugated diolefin having not more than six carbon atomsper molecule and a rosin acid, the weight ratio of said rosin acid tosaid liquid polymer not exceeding 1:1.

10. A rubber vulcanizing composition consisting essentially of anadmixture of a liquid copolymer of butadiene and styrene with a rosinacid.

11. A rubber vulcanizing composition consisting essentially of anadmixture of a liquid polymer prepared by emulsion polymerization of aconjugated diolefin having not more than 6 carbon atoms per molecule anda rosin acid.

12. A rubber vuicani zing composition result cule with 0.3 to 1 part byweight of a rosin acid..

13. The composition 01 claim 12 in which the dioleiin is 1,3-butadiene.

WALTER A. scams. 7

10 References Cited in theiiiie of this patent UNITED STATES PATENTSNumber Name Date Bjerregaard May 31, 1936 Rummeisburg Mar. 9, 1948Williams Dec. 28, 1948 Ralston Feb. 8, 1949 Pratt June 7, 1949

2. A RUBBER VULCANIZING COMPOSITION COMPRISING AN ADMIXTURE OF ONE PARTBY WEIGHT OF A LIQUID POLYMER OF CONJUGATED DIOLEFIN HAVING NOT MORETHAN 6 CARBON ATOMS PER MOLECULE WITH 0.3 TO 1 PART OF ROSIN ACID.